Questions 18 to 20 are based on the following passage. At the end of the passage, you will be given 15 seconds to answer the questions.
Now listen to the passage.
Which of the following statements is TRUE according to the passage

A．Scientists have developed a new drag to kill HIV virus.
B．Scientists have found a new treatment to prevent the spread of HIV.
C．Scientists have proven that HIV does cause the disease AIDS.
D．Scientists have found that the amount of virus in the blood affect the risk for HIV.